In 3GPP Long-Term Evolution (LTE) networks, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of base stations, e.g., evolved Node-Bs (eNBs) communicating with a plurality of mobile stations referred as user equipments (UEs). Recently, 3GPP systems, such as LTE-Advanced (LTE-A), improves spectrum efficiency by utilizing diverse deployments in a heterogeneous network topology, which means the maximum transmit power, the operating frequency, and the deployment location and density of eNBs can be very different. One possible deployment scenario is to utilize the different characteristics of carriers an operator has, e.g., joint operation of Frequency Division Duplex (FDD) and Time Division Duplex (TDD) carriers.
In a conventional FDD-TDD network, FDD carrier and TDD carrier work independently. For a conventional dual mode UE, the UE should be capable to operate in either FDD mode or TDD mode where “operate” means receiving and transmitting simultaneously in the case of FDD or one at a time in the case of TDD. Once the operating mode is determined, UE should behave like the operation in single mode case. In other words, conventional dual mode UEs have TDD and FDD RFs, while baseband capability is similar to single mode capable UEs. The protocol stack at UE side is equipped with one radio resource control (RRC), one packet data convergence protocol (PDCP), one radio link control (RLC), and a common media access control (MAC) with a hybrid automatic repeat request (HARQ) entity. Once the operation mode is chosen, the HARQ entity should be associated to that operation mode.
In a future FDD-TDD network, joint operation between FDD and TDD carriers to fully utilize the different characteristics can be expected. New characteristics of FDD-TDD operations should be considered and the associated enhancements are desired.